1. Field of the Invention
The present invention relates generally to abrasive waterjet cutting and disposal of radioactive material. In particular, the present invention relates to systems and processes that separate waterjet abrasive material from high level radioactive material cut by an abrasive waterjet process to minimize the amount of high level radioactive material for handling and disposal.
2. Description of the Related Art
Abrasive waterjet cutting is a process where a high pressure water source is forced through a nozzle and mixed with an abrasive medium. The high speed jet of water is dynamically unstable and breaks into small droplets that accelerate the solid abrasive particles. This high velocity abrasive slurry micro-machines a workpiece by causing erosion, shearing and failure due to rapidly changing localized stresses. The workpiece particles and abrasive particles are mixed as a result of the cutting process.
The abrasive waterjet cutting process requires several times the mass and volume of abrasive particles to perform the cut than are removed from the workpiece in the kerf of the cut. Therefore, when cutting radioactive materials, the mixture of the abrasive particles and workpiece particles represents an increased volume of high level radioactive material that must be handled and stored.
Waterjet cutting processes are commonly used during the dismantling of nuclear reactors. For example, waterjet cutting processes are often used on radioactive components, such as nuclear reactor internals, vessels, and other activated or contaminated materials and structures. These radioactive components are normally cut using a waterjet cutting process in a reactor vessel cavity, spent fuel pool or other underwater pool or cell.
The mixture of waterjet abrasive material and high level radioactive material removed during watejet cutting processes is considered unstable unless it is captured and stored in high integrity containers. The handling and storage of large volumes of such radioactive material is expensive and takes up a large amount of the limited space available for storing the material. Thus, there is a need for a system that separates non-radioactive abrasive material from the high level radioactive material so that the materials can be disposed of separately, thereby reducing handling concerns and disposal costs.
It is an object of the present invention to provide a system for separating a sufficient amount of radioactive material from non-radioactive material in a fluid stream to reduce the volume and cost of disposal of radioactive waste.
It is a further object of the present invention to provide a magnetic filtration system that removes a magnetic material from a fluid stream containing both magnetic and nonmagnetic waste materials to reduce the volume and cost of disposal of radioactive waste.
It is yet a further object of the present invention to provide a system that separates waterjet abrasive material from radioactive material cut by an abrasive waterjet process, whereby the radioactive material can be handled and stored separately from the abrasive material to minimize handling and disposal costs.
It is a still further object of the present invention to provide a magnetic filtration system that removes both abrasive material and radioactive cut material from a fluid stream using a magnetic filter where differentiation between the materials based on magnetic susceptibilities is not possible or practical, thereby minimizing secondary waste caused by the use of consumable cartridge filters.
According to a broad aspect of the present invention, a magnetic filtration system is provided for separating radioactive cut material from a fluid stream containing a mixture of the radioactive cut material and a nonradioactive abrasive cutting material. The system comprises a magnetic filter in fluid communication with the fluid stream. The magnetic filter has a first outlet for discharging material having a high magnetic susceptibility and a second outlet for discharging material having a low magnetic susceptibility. By selecting an abrasive cutting material having a different magnetic susceptibility than the radioactive material being cut, the magnetic filter can separate the abrasive cutting material from the radioactive cut material.
The abrasive cutting material can be a cast steel, stainless steel, shot or other material having a high magnetic susceptibility relative to the radioactive material being cut. Alternatively, the abrasive cutting material can be a garnet, alluvial or other material having a low magnetic susceptibility if the radioactive material being cut has a high magnetic susceptibility. In cases where the abrasive and the radioactive material being cut both have high magnetic susceptibility, the magnetic filter can be used to capture both the abrasive and radioactive material, thereby minimizing or eliminating secondary waste caused by the use of consumable cartridge filters.
According to another broad aspect of the present invention, a closed-loop filtration system is provided for removing radioactive particulate from a volume of fluid. The filtration system comprises: an enclosure submerged in a fluid volume for isolating a portion of the fluid volume from a remainder of the fluid volume; a capture structure for capturing abrasive cutting material and radioactive cut particulate generated within the enclosure; and a separating arrangement in fluid communication with the capture structure for receiving a fluid stream containing the abrasive cutting material and the radioactive cut particulate, the separating arrangement comprising a filter for separating the abrasive cutting material from the radioactive cut particulate, and an outlet that returns the fluid back into the enclosure.
The closed-loop filtration system according to this aspect of the invention has a magnetic filter for separating the abrasive cutting material from the radioactive cut material. The abrasive cutting material is selected so that it has a different magnetic susceptibility than the radioactive material to be cut, thereby allowing the magnetic filter to separate the high level radioactive materials from the low level abrasive materials for separate handling and disposal.
A filtering arrangement is placed in fluid communication with the magnetic separating arrangement. The filtering arrangement comprises a plurality of filters that remove the radioactive cut particulate from the fluid stream in multiple stages according to a size of the particulate. After filtering, the fluid from the fluid stream is returned to the isolated portion of the fluid volume in a closed-loop fashion.
According to another broad aspect of the present invention, a method of separating radioactive cut material from nonradioactive abrasive material is provided, comprising the steps of: determining a magnetic susceptibility of a radioactive material to be cut; selecting an abrasive material to be used with a waterjet cutting tool such that the abrasive material has a different magnetic susceptibility than the radioactive material to be cut; capturing a mixture of radioactive cut material and nonradioactive abrasive material generated during operation of the waterjet cutting tool; and separating the radioactive cut material from the nonradioactive abrasive material using a magnetic filter. The step of selecting an abrasive cutting material comprises selecting an abrasive cutting material with a high magnetic susceptibility if the radioactive cut material has a low magnetic susceptibility, and selecting an abrasive cutting material with a low magnetic susceptibility if the radioactive cut material has a high magnetic susceptibility.
Numerous other objects of the present invention will be apparent to those skilled in this art from the following description wherein there is shown and described a preferred embodiment of the present invention, simply by way of illustration of one of the modes best suited to carry out the invention. As will be realized, the invention is capable of other different embodiments, and its several details are capable of modification in various obvious aspects without departing from the invention. Accordingly, the drawings and description should be regarded as illustrative in nature and not restrictive.